In a mobile communication system, a handover is a process for switching from an original radio channel to a new radio channel when a UE (user equipment) moves from a coverage area of a BS (base station) to a coverage area of another BS during a period when the UE communicates with a network side.
Currently, in a UMTS (universal mobile telecommunications system) system, the handover is classified into an intra-system handover and an inter-system handover. The intra-system handover refers to that both an original cell used by the UE and a target cell to which the UE is handed over are cells in the UMTS system. The inter-system handover refers to a handover between a cell in the UMTS system and a cell in other radio system. In the prior art, an inter-system handover between the UMTS system, a GSM (global systems for mobile communication) system, and an LTE (long term evolution) system is supported.
LTE is a next-generation mobile communication standard which is being formulated currently by the 3GPP (3rd generation partnership project), aiming to provide a low-cost network which can lower network delay, increase a data rate and improve system capacity and coverage. In an overlapping coverage area or at a junction between a UMTS network and an LTE network, to better meet user demands, a user in the UMTS system may be migrated to the LTE system through the inter-system handover.
A UMTS-to-LTE system handover process mainly involves network entities, such as an RNC (radio network controller), an SGSN (serving GPRS support node), an MME (mobility management entity), an eNB (evolved Node B) and so on. An important step is that a source node RNC correctly sends a handover request to a target node eNB through a core network.
When determining to hand over a UE to the LTE network, the RNC sends a relocation required message to an SGSN, which includes a parameter and a Target ID (a target node identity) of the inter-system handover. Then, the SGSN forwards, according to the Target ID identity in the message, the handover request to a target MME through a forward relocation request message. The target MME then determines a target eNB according to the Target ID identity in the Forward Relocation Request message, and sends a handover request message to the target eNB to request establishment of required handover resources.
The Target ID in the foregoing message is a basis on which the SGSN addresses the target MME and the target MME addresses the target eNB. According to a different target system of a handover, the Target ID is classified into a Target RNC ID (target radio network controller identity), a Cell Global ID (cell global identity) and a Target eNB ID (target long term evolution base station identity). The Target RNC ID is used for a UMTS-to-UMTS handover, the Cell Global ID is used for a UMTS-to-GSM handover, and the Target eNB ID is used for a UMTS-to-LTE handover.
In a UMTS-to-LTE system handover, the Target ID needs to be set to the Target eNB ID. However, in an existing network, an SGSN that cannot identify the Target eNB ID exists. Therefore, the RNC may first convert a target node Target eNB ID into a Target RNC ID (called Corresponding RNC ID), and then the target MME restores the Corresponding RNC ID to a real Target eNB-ID according to a corresponding conversion rule. Through this kind of conversion strategy, the SGSN and the target MME can correctly forward a handover request to a target eNB node.
However, currently, there is still no rule for converting the Target eNB ID and the Corresponding RNC ID.